The present invention relates to a process and an apparatus for producing a laminate for electronic parts such as ceramic capacitors. More specifically, it relates to a process and an apparatus capable of producing a multi-layer laminate for electronic parts with a high output on an industrial scale.
In recent years, in the field of electronic parts, along with a tendency toward high-density surface mounting, it has been desired to reduce the sizes of laminate electronic parts such as laminate ceramic capacitors, laminate varistors, laminate filters and laminate piezoelectric elements and to improve the functions of these laminate electronic parts. A laminate ceramic capacitor is taken as an example hereinafter.
A laminate ceramic capacitor comprises a plurality of dielectric ceramic layers, a plurality of internal electrodes formed between respective adjacent ceramic layers and external electrodes connected to the respective internal electrodes at the ends of the dielectric ceramic layers.
Heretofore, the laminate ceramic capacitor has been produced by the following process.
A ceramic green sheet is prepared by casting a ceramic slurry over a stainless steel belt or the like into a sheet-form by a doctor blade method, and a conductive paste containing a metal which will become internal electrodes, such as palladium, silver-palladium or nickel, is coated on the ceramic green sheet surface to form predetermined electrode patterns by such a method as screen printing or the like. Generally, a plurality of laminate ceramic capacitors are produced by first forming a plurality of electrode patterns on a single green sheet, then laminating the second green sheet thereon, press-bonding the laminate in a thickness direction by a press to form the same patterns as above on the second green sheet, successively repeating the lamination and patterns-formation of the third and subsequent green sheets similarly to the second green sheet to obtain a final laminate and cutting the obtained laminate in the succeeding step. A wet or dry isotactic press is used as a press.
The obtained press-bonded laminate is cut so as to give laminates for obtaining individual laminate ceramic capacitors, the binder is removed from each laminate obtained by cutting, and the laminate is baked to obtain a sintered product. Thereafter, the external electrodes connected to the internal electrodes are baked to produce a laminate ceramic capacitor.
It has recently been desired to reduce the thickness of a ceramic laminate and increase the number of layers of the laminate so as to obtain a small-size and large-capacity laminate electronic part.
However, in an apparatus for producing a laminate electronic part by laminating together a plurality of ceramic green sheets as described above, an increase in the number of ceramic green sheets for a reduction in the thickness and an increase in the number of layers of a ceramic laminate requires a lot of time for the production of a single laminate.
Consequently, it has been desired to develop a laminate production apparatus which can improve productivity and differs from the apparatus for producing a laminate electronic part by cutting a ceramic green sheet to a predetermined shape and laminating a plurality of the ceramic green sheets as described above.
JP-A 4-500835 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a thin self-supporting unprocessed compressed material which contains an inorganic substance and a binder and has a thickness of less than 25xcexcm, wherein the binder as a thin layer material is a polymer having a weight average molecular weight of 400,000 or more, the polymer forms a thermally reversible gelation system having a gelation point and a melting point higher than room temperature in an appropriate solvent, and the volume fraction of the inorganic substance is 45% or more based on the total amount of the binder and the inorganic substance. This publication discloses a multi-layer magnetic capacitor as an example of this unprocessed compressed material but does not teach a process and an apparatus for producing the same.
It is an object of the present invention to provide an apparatus for producing a laminate for electronic parts such as ceramic capacitors using a self-supporting green sheet containing inorganic powder and an organic binder.
It is another object of the present invention to provide an apparatus capable of producing a multi-layer laminate for electronic parts using a self-supporting green sheet containing inorganic powder and an organic binder with a high output on an industrial scale.
It is still another object of the present invention to provide a process for producing a laminate for electronic parts such as a ceramic capacitor, particularly a multi-layer laminate, industrially advantageous.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by an apparatus for producing a laminate for electronic parts (may be referred to as xe2x80x9cfirst production apparatus of the present inventionxe2x80x9d hereinafter) which comprises:
(1) a feed unit for unrolling a self-supporting green sheet which contains inorganic powder and an organic binder;
(2) a columnar roll for taking up and laminating the self-supporting green sheet;
(3) a fixing unit for fixing the layers of the green sheet taken up by the columnar roll so that they do not shift out of alignment from one another;
(4) a pattern forming unit for forming an internal conductive layer having a predetermined pattern on the green sheet taken up by the columnar roll; and
(5) a pattern positioning unit for positioning the same pattern on the green sheet G2 of the next cycle to be laminated adjacently onto the green sheet G1 as a predetermined pattern on the green sheet G1 of the previous cycle taken up by the columnar roll with respect to the predetermined pattern on the green sheet G1.
Secondly, the above objects and advantages of the present invention are attained by an apparatus for producing a laminate for ceramic capacitors (to be referred to as xe2x80x9csecond production apparatus of the present inventionxe2x80x9d hereinafter) which comprises:
(1) a feed unit for unrolling a self-supporting green sheet which contains ceramic powder and an organic binder;
(2) a columnar roll for taking up and laminating the self-supporting green sheet;
(3) a fixing unit for fixing the layers of the green sheet taken up by the columnar roll so that they do not shift out of alignment from one another;
(4) a press-bonding unit for close-bonding together the layers of the green sheet taken up by the columnar roll;
(5) a pattern forming unit for forming an internal conductive layer having a predetermined pattern on the green sheet taken up by the columnar roll; and
(6) a pattern positioning unit for positioning the same pattern on the green sheet G2 of the next cycle to be laminated adjacently onto the green sheet G1 as a predetermined pattern on the green sheet G1 of the previous cycle taken up by the columnar roll with respect to the predetermined pattern on the green sheet G1.
Thirdly, the above objects and advantages of the present invention are attained by an apparatus for producing a laminate for electronic parts (may be referred to as xe2x80x9cthird production apparatus of the present inventionxe2x80x9d hereinafter) which comprises:
(1) a feed unit for unrolling a self-supporting green sheet which contains inorganic powder and an organic binder;
(2) a columnar roll for taking up and laminating the self-supporting green sheet;
(3) a fixing unit for fixing the layers of the green sheet taken up by the columnar roll so that they do not shift out of alignment from one another; and
(4) a pattern positioning unit for positioning the same pattern on the green sheet G2 of the next cycle to be laminated adjacently onto the green sheet G1 as a predetermined pattern on the green sheet G1 of the previous cycle taken up by the columnar roll with respect to the predetermined pattern on the green sheet G1.
Fourthly, the above objects and advantages of the present invention are attained by a process for producing a laminate for electronic parts by winding a self-supporting green sheet which contains inorganic powder and an organic binder and has a predetermined pattern for forming an internal conductive layer formed thereon round a columnar roll several times (may be referred to as xe2x80x9cfirst production process of the present inventionxe2x80x9d hereinafter), wherein
the green sheet G2 of the next cycle is wound round the green sheet G1 of the previous cycle to ensure that a fixed positional relationship is established between a predetermined pattern formed on the green sheet G1 wound round the columnar roll and the same pattern formed on the green sheet G2 as the predetermined pattern on the green sheet G1.
Fifthly, the above objects and advantages of the present invention are attained by a process for producing a laminate for electronic parts by winding a self-supporting green sheet which contains inorganic powder and an organic binder and has a predetermined pattern for forming an inner conductive layer formed thereon round a columnar roll several times (may be referred to as xe2x80x9csecond production process of the present inventionxe2x80x9d hereinafter), wherein either one or both of the following steps is/are carried out in the order named after the step of winding the green sheet G2 of the next cycle round the green sheet G1 of the previous cycle to ensure that a fixed positional relationship is established between a predetermined pattern formed on the green sheet G1 wound round the columnar roll and the same pattern formed on the green sheet G2 of the next cycle as the predetermined pattern on the green sheet G1;
the step of thermally relaxing the obtained laminate wound round the columnar roll to control shrinkage in the lamination plane at 200xc2x0 C. to 1% or less; and
the step of hydrostatically pressing the laminate wound round the columnar roll.
Finally, the above objects and advantages of the present invention are attained by a process for producing a ceramic capacitor from a laminate formed by winding a self-supporting green sheet which contains ceramic powder and ultra high molecular weight polyethylene round a columnar roll several times (may be referred to as xe2x80x9cthird production process of the present inventionxe2x80x9d hereinafter), wherein
the green sheet G2 of the next cycle is wound round the green sheet G1 of the previous cycle to ensure that a fixed positional relationship is established between a predetermined pattern formed on the green sheet G1 wound round the columnar roll and the same pattern formed on the green sheet G2 of the next cycle as the predetermined pattern on the green sheet G1; the predetermined pattern is formed on the green sheet G1 before the self-supporting green sheet G2 of the next cycle is wound round the self-supporting green sheet G1 having no predetermined pattern for forming an internal conductive layer; the predetermined pattern consists of a single row or a plurality of rows of quadrilaterals arranged linearly at intervals, each of which is shorter than the length of one side parallel to the arrangement direction of the quadrilateral; and the green sheet G2 is wound round the green sheet G1 by locating each of the quadrilaterals of the green sheet G2 over the interval between the adjacent quadrilaterals of the green sheet G1 to establish the above fixed positional relationship between the predetermined patterns of the adjacent green sheets G1 and G2.
The above production apparatuses and processes of the present invention will be described hereinunder.